You need the graflok back adapter to use 2x3 grafloks. Theres one on ebay for $150. No thanks. I'll make a 4x5 adapter instead. I have a Mamiya Press Model G for 2x3 work.

The focussing tabs are notorious for breaking. I contacted SK Grimes, in anticipation, as he makes replacement focussing rings. $250! Eeek. Just going to be extremely careful with my XL